4G
4G refers to the fourth generation of cellular network technology, introduced in the late 2000s and early 2010s. Compared to preceding third-generation technologies, 4G has been designed to support all-IP communications and broadband services, and eliminates circuit switching in voice telephony. It also has considerably higher data bandwidth compared to 3G, enabling a variety of data-intensive applications such as high-definition media streaming and the expansion of Internet of Things applications.
The earliest deployed technologies marketed as "4G" were Long Term Evolution, developed by the 3GPP group, and Mobile Worldwide Interoperability for Microwave Access, based on IEEE specifications. These provided significant enhancements over previous 3G and 2G.
Technical overview
In November 2008, the International Telecommunication Union-Radio communications sector specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced specification, setting peak speed requirements for 4G service at 100 megabits per second for high mobility communication and 1 gigabit per second for low mobility communication.Since the first-release versions of Mobile WiMAX and LTE support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers. According to operators, a generation of the network refers to the deployment of a new non-backward-compatible technology. On December 6, 2010, ITU-R recognized that these two technologies, as well as other beyond-3G technologies that do not fulfill the IMT-Advanced requirements, could nevertheless be considered "4G", provided they represent forerunners to IMT-Advanced compliant versions and "a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed". Both the original LTE and WiMAX standards had previously sometimes been referred to as 3.9G/3.95G. The ITU's new definition for 4G also included Evolved High Speed Packet Access.
Mobile WiMAX Release 2 and LTE Advanced
are IMT-Advanced compliant backwards compatible versions of the above two systems, standardized during the spring 2011, and promising speeds in the order of 1 Gbit/s. In January 2012, the ITU backtracked on its previous definition for 4G, claiming that Mobile WiMAX 2 and LTE Advanced are "true 4G" while their predecessors are "transitional" 3G-4G.
As opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but instead relies on all-Internet Protocol based communication such as IP telephony. As seen below, the spread spectrum radio technology used in 3G systems is abandoned in all 4G candidate systems and replaced by OFDMA multi-carrier transmission and other frequency-domain equalization schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation. The peak bit rate is further improved by smart antenna arrays for multiple-input multiple-output communications.
Background
In the field of mobile communications, a "generation" generally refers to a change in the fundamental nature of the service, non-backwards-compatible transmission technology, higher peak bit rates, new frequency bands, wider channel frequency bandwidth in Hertz, and higher capacity for many simultaneous data transfers.New mobile generations have appeared about every ten years since the first move from 1981 analog to digital transmission in 1992. This was followed, in 2001, by 3G multi-media support, spread spectrum transmission and a minimum peak bit rate of 200 kbit/s, in 2011/2012 to be followed by "real" 4G, which refers to all-IP packet-switched networks giving mobile ultra-broadband access.
While the ITU has adopted recommendations for technologies that would be used for future global communications, they do not actually perform the standardization or development work themselves, instead relying on the work of other standard bodies such as IEEE, WiMAX Forum, and 3GPP.
In the mid-1990s, the ITU-R standardization organization released the IMT-2000 requirements as a framework for what standards should be considered 3G systems, requiring 2000 kbit/s peak bit rate. The fastest 3G-based standard in the UMTS family is the HSPA+ standard, which has been commercially available since 2009 and offers 21 Mbit/s downstream without MIMO, i.e. with only one antenna, and in 2011 accelerated up to 42 Mbit/s peak bit rate downstream using either DC-HSPA+ or
2x2 MIMO. In theory speeds up to 672 Mbit/s are possible, but have not been deployed yet. The fastest 3G-based standard in the CDMA2000 family is the EV-DO Rev. B, which is available since 2010 and offers 15.67 Mbit/s downstream.
In 2008, ITU-R specified the IMT Advanced requirements for 4G systems.
Frequencies for 4G+ LTE networks
IMT-Advanced requirements
This article refers to 4G using IMT-Advanced, as defined by ITU-R. An IMT-Advanced cellular system must fulfill the following requirements:- Be based on an all-IP packet switched network.
- Have peak data rates of up to approximately 100Mbit/s for high mobility such as mobile access and up to approximately 1Gbit/s for low mobility such as nomadic/local wireless access.
- Be able to dynamically share and use the network resources to support more simultaneous users per cell.
- Use scalable channel bandwidths of 5–20 MHz, optionally up to 40 MHz.
- Have peak link spectral efficiency of 15bit/s·Hz in the downlink, and 6.75bit/s·Hz in the up link.
- System spectral efficiency is, in indoor cases, 3bit/s·Hz·cell for downlink and 2.25bit/s·Hz·cell for up link.
- Smooth handovers across heterogeneous networks.
- LTE Advanced standardized by the 3GPP
- 802.16m standardized by the IEEE
The first set of 3GPP requirements on LTE Advanced was approved in June 2008. LTE Advanced was standardized in 2010 as part of Release 10 of the 3GPP specification.
Some sources consider first-release LTE and Mobile WiMAX implementations as pre-4G or near-4G, as they do not fully comply with the planned requirements of 1Gbit/s for stationary reception and 100Mbit/s for mobile.
Confusion has been caused by some mobile carriers who have launched products advertised as 4G but which according to some sources are pre-4G versions, commonly referred to as 3.9G, which do not follow the ITU-R defined principles for 4G standards, but today can be called 4G according to ITU-R. Vodafone Netherlands for example, advertised LTE as 4G, while advertising LTE Advanced as their '4G+' service. A common argument for branding 3.9G systems as new-generation is that they use different frequency bands from 3G technologies; that they are based on a new radio-interface paradigm; and that the standards are not backwards compatible with 3G, whilst some of the standards are forwards compatible with IMT-2000 compliant versions of the same standards.
System standards
IMT-2000 compliant 4G standards
As of October 2010, ITU-R Working Party 5D approved two industry-developed technologies for inclusion in the ITU's International Mobile Telecommunications Advanced program, which is focused on global communication systems that will be available several years from now.LTE Advanced
is a candidate for IMT-Advanced standard, formally submitted by the 3GPP organization to ITU-T in the fall 2009, and as of 2013 has been released to the public.The target of 3GPP LTE Advanced is to reach and surpass the ITU requirements. LTE Advanced is essentially an enhancement to LTE. It is not a new technology, but rather an improvement on the existing LTE network. This upgrade path makes it more cost effective for vendors to offer LTE and then upgrade to LTE Advanced which is similar to the upgrade from WCDMA to HSPA. LTE and LTE Advanced will also make use of additional spectrums and multiplexing to allow it to achieve higher data speeds. Coordinated Multi-point Transmission will also allow more system capacity to help handle the enhanced data speeds.| LTE Advanced | |
| Peak download | 1000 Mbit/s |
| Peak upload | 500 Mbit/s |
IEEE 802.16m or WirelessMAN-Advanced
The IEEE 802.16m or WirelessMAN-Advanced evolution of 802.16e is under development, with the objective to fulfill the IMT-Advanced criteria of 1 Gbit/s for stationary reception and 100 Mbit/s for mobile reception.Forerunner versions
Long Term Evolution (LTE)
The pre-4G 3GPP Long Term Evolution technology is often branded "4G – LTE", but the first LTE release does not fully comply with the IMT-Advanced requirements. LTE has a theoretical net bit rate capacity of up to 100 Mbit/s in the downlink and 50 Mbit/s in the uplink if a 20 MHz channel is used — and more if multiple-input multiple-output, i.e. antenna arrays, are used.The physical radio interface was at an early stage named High Speed OFDM Packet Access, now named Evolved UMTS Terrestrial Radio Access.
The first LTE USB dongles do not support any other radio interface.
The world's first publicly available LTE service was opened in the two Scandinavian capitals, Stockholm and Oslo on December 14, 2009, and branded 4G. The user terminals were manufactured by Samsung. As of November 2012, the five publicly available LTE services in the United States are provided by MetroPCS, Verizon Wireless, AT&T Mobility, U.S. Cellular, Sprint, and T-Mobile US.
T-Mobile Hungary launched a public beta test on 7 October 2011, and has offered commercial 4G LTE services since 1 January 2012.
In South Korea, SK Telecom and LG U+ have enabled access to LTE service since 1 July 2011 for data devices, slated to go nationwide by 2012. KT Telecom closed its 2G service by March 2012 and completed nationwide LTE service in the same frequency around 1.8 GHz by June 2012.
In the United Kingdom, LTE services were launched by EE in October 2012, by O2 and Vodafone in August 2013, and by Three in December 2013.
| LTE | |
| Peak download | 150 Mbit/s |
| Peak upload | 50 Mbit/s |